Guide to the Elements - Carbon

(2/11/2009) - Unlike some elements, your tantalums and rubidiums, carbon has nearly universal name recognition – and with good reason.  Not only is carbon is one of the essential building blocks of life as we know it, but most of the energy sources that fuel modern industry are carbon-based, and carbon-based pollution is one of the most problematic pollutants humans emit today. 

(In this article, I only focus on a few aspects of carbon that I didn’t know about before.  I didn’t want to bore you with stuff you probably know.)

What is carbon? – Carbon has six protons, four valence electrons, and it is the fourth most abundant element in the universe.  Carbon’s most important characteristic is its ability to bind to itself (and hydrogen) to create self-supporting carbon rings that can be joined together in nearly infinite stretches.

Pure carbon is found in many different states or allotropes, which can roughly be divided into four categories – diamond, graphite, vegetal carbon, and black fumes.  Diamond and graphite are crystalline, while vegetal carbon is amorphous and black fumes are gaseous. 

Caption - Different types of carbon, including A) Diamond
B) Graphite G) Amorphous Carbon, and H) Carbon Nanotube.

Where does carbon come from? – While the earth’s crust is only 0.032% carbon, carbon compounds are abundant on the planet’s surface and exist in concentrated pockets below the earth’s surface in coal, petroleum, shale oil, tar and natural gas. 

Diamond is the rarest of the four carbon allotropes.  To make up for this fact, we’ve learned to manufacture synthetic diamonds, which make up 99% of all diamonds used for industrial purposes in the United States and 88% worldwide. 

Natural graphite isn’t mined in the United States.  Most of the world’s graphite reserves are in China, which is also the world’s largest producer of graphite.  According to the USGS, about a million tons of graphite are mined and consumed every year.  World graphite reserves total 86 million tons, while the reserve base stands at 210 million tons.  In the future, they say large-scale fuel-cell applications could consume as much graphite as all other uses combined.  Synthetic graphite is produced using petroleum coke, a byproduct of refining.

What is carbon used for? – Carbon is part of more compounds than all other elements combined.  We eat it, wear it, live in buildings made of it, and fuel our cars, planes, ships, and (some) trains with it. 

While best known for use in jewelry, diamonds also have numerous industrial purposes that take advantage of diamond’s hardness (it is the hardest known natural material) and being a natural semiconductor.  Diamonds are used to make computer chips, in construction, machinery manufacturing, mining, stone cutting and polishing, and transportation.  Graphite is used in pencils, refractory applications, brake linings, batteries, foundry operations, and lubricants.

Can carbon be recycled? – Yes and no.  Some carbon compounds, like wood pulp, can be recycled at least several times before it is no longer useful.  The world’s carbon cycle recycles carbon over and over again, in and out of countless biological organisms. 

However, many of the most useful carbon compounds cannot be recycled without huge investments of energy and time.  In theory, the CO2 we release from burning fossil fuels could one day be reabsorbed by a plant, which could then die and eventually be turned into another fossil fuel.  However, this process would take millions and millions of years.  Currently, we can recycle some CO2 in bio-fuels.  While we can produce these faster than it takes to produce traditional fossil fuels, ethanol, bio-diesel, etc. do not contain as much energy per weight.  

Does carbon present any environmental concerns? – The carbon compound CO2 is the most prevalent greenhouse gas present in the atmosphere.  Its role in global warming is a well-known threat to the world’s predominate climate from the past 12,000 years. 

There are also some carbon-based wastes that pose environmental hazards, such as the fly ash collected from coal-fired plants. 

Photo Credits - Carleton University and Wikipedia